Refuges Play Critical Role in Maintaining Durability of Bt Hybrids

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Pyramided corn hybrids (SmartStax) are making their debut this planting season with a refuge reduction from 20% to 5% in the Corn Belt. The increased use of Bt hybrids as the foundation of corn insect management programs makes establishing refuge requirements critical.

“Refuges play a key role in delaying or preventing the development of resistant populations of key insect pests such as the European corn borer or western corn rootworm,” says Mike Gray, University of Illinois Extension entomologist. “We have been fortunate that field-level resistance has not developed for either of these two species despite the widespread adoption of this impressive technology.”

In 2009, nearly 60% of all corn planted in Illinois was a stacked hybrid. These stacks include corn hybrids that express Bt proteins targeted against the lepidopteran complex (European corn borers, black cutworms, western bean cutworms) and corn rootworms, as well as offer herbicide tolerance.

For 2010, the 5% refuge for SmartStax must be a structured refuge – seed mixtures cannot serve as this refuge. For producers who elect to plant other Bt hybrids, the 20% structured refuge requirement remains the same.

Based upon surveys of producers participating in the 2010 Corn and Soybean Classics, slightly fewer than 80% indicated they planted a refuge in 2009 according to suggested guidelines.

“Over time, as more pyramided hybrids become commercialized, I suspect that seed mixtures (transgenic and non-transgenic seed) will form the foundation of resistance management plans,” Gray says. “This will ensure grower compliance. And with the pyramided technology in place, it should help prolong the long-term durability of Bt hybrids.”

Many producers said they were receptive to the use of a seed blend as a refuge. A key concern regarding a seed mixture approach was the potential for significant insect injury to non-Bt seed and the inability to rescue injured plants. However, the convenience offered via a seed mixture refuge strategy seems to “trump” this concern for most producers up to a point, Gray says.

Approximately 90% indicated their willingness to use a seed blend that contained non-Bt seed in the 2-5% range. However, if non-Bt seed falls within the 6-10% range, interest in this approach falls below 60%.

Gray encourages producers to contact him if they experience any corn rootworm control problems when using Bt hybrids.

“Often corn rootworm larval damage goes unnoticed unless severe lodging occurs,” he says. “In many instances, this lodging is not detected until harvest occurs. Check the value of your investment in Bt corn this year. Grab a shovel and remove some corn roots from Bt as well as refuge areas of your fields. Mid-July is the best time to check for corn rootworm pruning, despite the heat and pollen.”